This invention relates to liquid silicone rubber compositions. More particularly, this invention relates to a liquid silicone rubber composition that yields a highly flame retardant cured product that also has excellent electrical properties such as tracking resistance, arc resistance, and erosion resistance. The invention additionally relates to a method for preparing the subject liquid silicone rubber composition.
Silicone rubbers are widely used in diverse applications because of their excellent heat resistance, excellent resistance to aging, and excellent electrical properties. However, a drawback to silicone rubbers is their flammability, and in response to this numerous compositions have been proposed to date that provide self-extinguishing (flame retardant) silicone rubbers. For example, Japanese Patent Publication Kokoku No. Sho 44-2591 (2,591/1969) teaches the composition afforded by blending a platinum compound flame retardant, such as chloroplatinic acid or a platinum-olefin complex, into a silicone rubber compound. However, the admixture of just a platinum compound provides only a small improvement in flame retardancy. This fact has resulted in the proposal of compositions that achieve improvements in the flame retardancy of silicone rubber through the combination of these platinum compounds and inorganic filler such as described in Japanese Patent Publication Kokoku No. Sho 47-21826 (21,826/1972) and Japanese Patent Publication Kokoku No. Sho 51-23979 (23,979/1976). Other tactics known for achieving additional improvements in the flame retardancy of the subject silicone rubber compositions consist of increasing the addition of the nonflammable inorganic filler component and reducing the addition of the flammable polyorganosiloxane component. Unfortunately, the silicone rubber compositions made by these tactics have very high viscosities and thus cannot be used in applications where fluidity is a critical factor, for example, as in injection molding.
Therefore, desired is a liquid silicone rubber composition that prior to its cure has a suitable fluidity and excellent moldability and that cures into highly flame retardant silicone rubber moldings with excellent electrical properties.
As a result of extensive investigations directed to solving the problems described above, the inventors have discovered that these problems can be solved by the admixture of specific additive components into a particular type of addition reaction-curing liquid silicone rubber composition. The present invention was achieved based on this discovery.
In specific terms, then, the object of the present invention is to provide a liquid silicone rubber composition that prior to its cure exhibits suitable fluidity and excellent moldability and that cures to give highly flame retardant silicone rubber moldings with excellent electrical properties and does so without sacrificing mechanical strength.